A 42-year-old woman presented with a chronic, vague, epigastric
pain. The physical examination was not contributory. Upper
gastrointestinal endoscopy was normal. The patient was treated with
proton pump inhibitors for 6 weeks but without any relief. A
contrast-enhanced (Omnipaque 100 ml, GE Healthcare, Chalfont St. Giles,
U.K.) computed tomography (CT; SOMATOM Emotion 6, Siemens Healthcare,
Malvern, PA) exam of the abdomen and pelvis was performed on a 6-slice
helical scanner after labeling the bowel with dilute, iodinated
contrast.

IMAGING FINDINGS

CT (Figures 1-4) revealed the classic "bowel within
bowel" configuration with intervening mesenteric vessels in the
region of the proximal transverse colon (right hypochondrium of the
patient) over a segment of approximately 8 cm with a 2.5 cm rounded fat
density lesion at its apex (Hounsfield unit values of -60 to -130). The
intervening bowel layers showed normal wall enhancement. There was no
dilatation of the proximal bowel. The solid abdominal organs were
normal. There was no ascitis.

DIAGNOSIS

Colocolic intussusception in the hepatic flexure and proximal
transverse colon with a 2.5 cm lipoma.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

FOLLOW-UP

Corresponding ultrasound images (Figures 5 and 6) showed the
classical pseudokidney appearance of intussusception and a rounded
echogenic lipoma at the apex.

The bowel was prepared prior to surgery and a supraumbilical
laparotomy was performed. The intussusception was reduced and the
involved segment at the hepatic flexure was resected. Biopsy of the
resected segment revealed a lipoma of the hepatic flexure.

[FIGURE 4 OMITTED]

DISCUSSION

Intussusception can be classified according to location or
underlying etiology. It occurs either in the small bowel or the colon.
The underlying etiology is neoplastic (benign or malignant),
non-neoplastic or idiopathic. About 80% to 90% of intussusceptions in
adults are secondary to an underlying pathology, with approximately 65%
due to benign or malignant neoplasm. Non-neoplastic processes constitute
15% to 25% of cases, while idiopathic or primary intussusceptions
account for about 10%. Intussusception arises in the small bowel in two
thirds of cases. (1,2)

[FIGURE 5 OMITTED]

Lipomas are the second most common benign tumors of the colon after
adenomas. These tumors are composed of well-defined adipose tissue with
a clearly demarcated fibrous support structure. They have a submucous
location in 90% of cases. Lipomas can be located anywhere along the
digestive tract but they are most common in the colon. Within the colon,
50% are found in the caecum and ascending colon. The occurrence of
distal-colon lipoma is rare. Sigmoid lipoma is extremely rare. (3)

Intussusception can be confidently diagnosed on CT because of its
virtually pathognomonic appearance. It appears as a complex soft-tissue
mass, consisting of the outer intussuscipiens and the central
intussusceptum. There is often an eccentric area of fat density within
the mass rep resenting the intussuscepted mesenteric fat, and the
mesenteric vessels are often visible within it. A rim of orally
administered contrast medium is sometimes seen encircling the
intussusceptum, representing coating of the opposing walls of the
intussusceptum and the intussuscipiens. The intussusception will appear
as a sausage-shaped mass when the CT beam is parallel to its
longitudinal axis, but will appear as a "target" mass when the
beam is perpendicular to the longitudinal axis of the intussusception.
While the appearance of intussusception is characteristic on CT, its
etiology cannot usually be established. Exceptions are lipoma, a long
intestinal tube and known abdominal metastatic disease. A lipoma serving
as a lead point is identified as a mass of fat density that does not
contain blood vessels. Mesenteric fat entrapped in an intussusception
also has fat density but has blood vessels coursing through it, and can
thus be distinguished from lipoma. (4)

[FIGURE 6 OMITTED]

Warshauer and Lee found that intussusceptions seen on CT that had a
neoplastic lead point were significantly longer and had a significantly
larger diameter than non-neoplastic ones. (5) They also found proximal
dilatation of the small bowel to be significantly more common in
intussusceptions with a neoplastic lead point.

The bowel loops proximal to the intussusception are usually of
normal calibre and are occasionally dilated, since intussusception in
adults only rarely presents as intestinal obstruction. (6) Although
intussusception in adults may be diagnosed by many other imaging
modalities, including barium enema, upper gastrointestinal series and
ultrasound, CT is clearly superior. In contrast to ultrasound, CT is not
affected by the presence of gas in the bowel and will clearly
demonstrate the intussusception, whether in the small bowel or in the
colon. Additional valuable information such as the presence of
metastatic disease or lymphadenopathy is readily obtained by CT and may
point to an underlying pathology.

Ultrasound imaging of this condition demonstrates several unique
appearances: on a transverse section one can see a "doughnut"
shape and on a longitiudinal section one can see a "bull's
eye" confirguation, and a pseudokidney finding is also typical.

CT findings also permit a presurgical evaluation of the degree of
vascular involvement caused by intussusception. The presence of gas
within the intussusceptum suggests perforation or gangrene, indicating
the need for an emergency operation.

In this patient, spiral CT showed a lipoma situated in the proximal
transverse colon, causing colocolic intussusception. The CT study helped
to determine the viability of the intussuscepted loop prior to surgery,
thus reducing the extent of surgical treatment and only the tumor was
removed. Multiplanar reconstructed spiral CT, allowed examination of the
intussusception and lipoma from various angles.

CONCLUSION

CT is a valuable tool in cases of intussusception due to colonic
lipoma. The most important factor for establishing the diagnosis is
awareness of the possibility of intussusception occurring in an adult
patient with abdominal symptoms, CT is then the examination of choice.